Data transmission method and apparatus in WLAN

ABSTRACT

A method for indicating a transmission opportunity (TXOP) duration in a wireless communication system includes generating, by a TXOP holder, a physical layer protocol data unit (PPDU). The PPDU includes a High Efficiency Signal field A (HE-SIGA), and the HE-SIGA includes a TXOP duration field. The TXOP duration field is used to indicate to other stations a remaining time for using a channel by a station. The TXOP duration field includes a first part which indicates a granularity used, and a second part which indicates the TXOP duration using the granularity indicated by the first part. The TXOP holder sends the generated PPDU.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/CN2017/071258, filed on Jan. 16, 2017, which claims priority to U.S. Provisional Application No. 62/278,437, filed on Jan. 14, 2016, and priority to U.S. Provisional Application No. 62/363,344, filed on Jul. 18, 2016. All of the afore-mentioned patent applications are hereby incorporated by reference in their entireties.

DEFINITION OF ABBREVIATIONS

HE: high efficiency

HE-SIGA: High Efficiency Signal field A

SU: single user

MU: multiple user

PPDU: physical layer protocol data unit

PHY: physical layer

MAC: medium access control layer

EDCA: enhanced distributed channel access

QoS: quality of service

SR: spatial reuse

DL: downlink

UL: uplink

NAV: network allocation vector

ACK: acknowledge

LGI: long guard interval

STF: short training field

LTF: long training field

SIG: signal field

RTS: request to send

L-SIG: non-HT signal field

L-STF: non-HT short training field

L-LTF: non-HT long training field

RL-SIG: repeated non-HT signal field

SIFS: short interframe space

TXOP: transmission opportunity

SS: simulation scenario

SLS: system level simulation

CF: contention free

CF-Poll: contention free poll

CF-END: contention free end

FIELD OF THE INVENTION

The present invention relates to the field of communications technologies, and more specifically, to a method for transceiving in a WLAN and an apparatus.

BACKGROUND OF THE INVENTION

Wireless Local Area Networks (WLAN) is a data transmission system. It uses radio frequency (RF) technology to replace the old twisted-pair copper wire formed by the local area network, making the wireless local area network can use a simple access architecture allows users through it, to achieve the purpose of information transmission. The development and application of WLAN technology has deeply changed people's communication way and working way, and brought people unprecedented convenience. With the wide application of intelligent terminals, the demand for data network traffic is increasing day by day.

WLAN development is inseparable from the development and application of its standards, including IEEE802.11 series is the main standard, there are 802.11, 802.11b/g/a, 802.11n, 802.11ac. In addition to 802.11 and 802.11b other standards are used Orthogonal Frequency Division Multiplexing, OFDM technology as the physical layer of the core technology.

SUMMARY OF THE INVENTION

In 802.11ax, the field of transmission opportunity (TXOP) duration was included in HE-SIGA of SU PPDU, DL MU PPDU or UL MU PPDU, in order to replace the Duration in MAC header in former standards. However the number of bit is still TBD.

The TXOP duration is the time remaining for a station (STA) to use a channel. For example, a STA sends a packet of 1 ms, which is not counted in the remaining time of using the channel by the STA, because the 1 ms has already been used. TXOP duration indicates the remaining time during which a channel is available for using by the station, such as 3 ms. There is a limit to the value of the remaining time.

Duration field in a MAC header has 16 bits (15 valid bits) in the units of 1 μs. It can indicate the maximum time duration of 32.767 ms.

In this application, we further discuss a solution which increases the efficiency of the indication of TXOP duration. In the method, the station generates a PPDU, which carries a TXOP field (TXOP duration) in the HE-SIGA of the PPDU, which is used for notifying the other station of the remaining time of using the channel by the station, wherein the TXOP field can be indicated in different granularities (units). The PPDU is sent by the station. In a example, the TXOP field occupies 7 bits, being indicated by two different granularities. For example, the two different granularities include 8 μs and 256 μs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of indication of TXOP duration;

FIG. 2 illustrates the performance degradation of the opt1, 2, 3 and fixed 64 μs;

FIG. 3 illustrates an embodiment of indication of TXOP duration;

FIG. 4 illustrates an embodiment of indication of TXOP duration;

FIG. 5 illustrates an embodiment of indication of TXOP duration;

FIG. 6 illustrates an embodiment of indication of TXOP duration;

FIG. 7 illustrates an system of indication of TXOP duration;

FIG. 8 illustrates an apparatus of indication of TXOP duration.

DESCRIPTION OF EMBODIMENTS

TXOP limits in EDCA

AP can set the policy of channel access with the EDCA Parameter Set element, where a TXOP limit is defined.

A TXOP limit has 16 bits in the unit of 32 μs. The default EDCA parameter of TXOP for each access category is as Table 1:

TABLE 1 TXOP limit For PHYs defined in Clause 18, For PHYs defined Clause 19, in Clause 16 and Clause 20, and Other AC CWmin CWmax AIFSN Clause 17 Clause 22 PHYs AC_BK aCWmin aCWmax 7 0 0 0 AC_BE aCWmin aCWmax 3 0 0 0 AC_VI (aCWmin + 1)/2 − 1 aCWmin 2 6.016 ms 3.008 ms 0 AC_VO (aCWmin + 1)/4 − 1 (aCWmin + 1)/2 − 1 2 3.264 ms 1.504 ms 0

A STA can also be granted a TXOP with QoS data frames of subtypes that include CF-Poll.

The time duration of the TXOP is carried in the 8-bit TXOP limit subfield of QoS field in MAC header. The range of time values is 32 μs to 8160 μs.

There are also different regulations for TXOP in different countries, such as 4 ms in Japan.

It is provided that 4.08 ms-16.32 ms is a reasonable range for TXOP limit for 802.11ax considering the efficiency and fairness among different BSS in the dense environment.

16.32 ms can support at least one pair of DL and UL PPDU in a cascading structure.

TXOP Unit

The smaller TXOP unit cost large number of bits in HE-SIGA.

There are only 13 or 14 bits in total left in the HE-SIGA of SU PPDU or DL MU PPDU.

Around 7˜9 bits can be used for TXOP duration considering the field of spatial reuse and other potential new fields, e.g. non-contiguous channel bonding.

3˜4 bits for SR.

2 bits for non contiguous channel bonding in DL MU PPDU.

The larger TXOP unit cost performance degradation due to NAV extension at 3rd party STA.

As shown in FIG. 1 (SLS evaluation), we observed that the NAV extension will not exceed 2 times of the TXOP unit, no matter the length of TXOP and how many packet exchanged within the TXOP.

IEEE SS2 (can be seen in TGax simulation scenarios document (11-14-0980)), 32 BSSs; ˜64 STAs/BSS (totally 2048 STAs in 32 BSSs, that is, about 64 STAs per BSS); Frequency Reuse factor=4;

20 MHz @5 GHz (in 5 GHz unlicensed band, the bandwidth is 20 MHz.); 2T×2R, wherein the T is short for Transmission antenna number, the R is short for Receiving antenna number.

Full buffer, 2 ms TXOP, RTS off

CF-END Off

TABLE 2 Unit (μs) Throughput (Mbps) Loss 1024 247.648 49.99% 512 331.483 33.05% 256 394.352 20.36% 128 439.931 11.15% 64 466.632 5.76% 32 481.309 2.80% 16 489.537 1.13% 1 (original) 495.153 0.00%

CF-END On

TABLE 3 unit (μs) Throughput (Mbps) Loss 1024 464.871 6.08% 512 466.109 5.83% 256 465.743 5.91% 128 464.396 6.18% 64 465.582 5.94% 32 479.736 3.08% 16 488.327 1.34% 1 (original) 494.983 0.00%

Considering the current numerology in 802.11ax, 4 μs˜32 μs is suitable for the minimum TXOP unit.

Maximum symbol duration of 16 μs Data symbol+LGI.

Maximum symbol duration of 8 μs for HE-STF, 16 μs for HE-LTF+LGI.

32 μs fixed preamble overhead of 802.11ax.

PPDU(L-STF+L-LTF+L-SIG+RL-SIG+HE-SIGA)

Multi-level TXOP indication

Smaller TXOP unit for shorter TXOP, larger unit for longer TXOP, in order to keep the similar relative loss.

E.g. 4 μs TXOP unit for TXOP length shorter than 128 μs, while 256 μs TXOP unit for TXOP length larger than 896 μs

The NAV extension can be alleviated by sending CF-end if the remaining time is larger than 68 μs (CF-END+SIFS).

In this application, a method to indicate TXOP duration in HE-SIGA is disclosed.

In order to achieve tradeoff between performance and overhead, 6 or 7 bits are used with multi-level indication.

Example 1 (Opt 1) Shown in Table 4

7 bits in total

2 bits indicate the TXOP unit: 4 μs/8 μs/16 μs/256 μs.

TABLE 4 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~124 μs 4 μs 01 00000~11111 128 μs~376 μs 8 μs 10 00000~11111 384 μs~880 μs 16 μs  11 00000~11111  896 μs~8832 μs 256 μs 

Example 2 (Opt 2) Shown in Table 5

7 bits in total, wherein 2 bits indicate the TXOP unit: 8 μs/16 μs/32 μs/512 μs.

TABLE 5 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs  8 μs 01 00000~11111 256 μs~752 μs  16 μs 10 00000~11111 768 μs~1760 μs 32 μs 11 00000~11111 1792 μs~17664 μs 512 μs 

Simplified Solutions

Example 3 (Opt 3), Shown in Table 6

6 bits in total, wherein 1 bit indicate the TXOP unit: 16 μs/512 μs.

TABLE 6 B1 B2~B6 TXOP range Unit 0 00000~11111 0 μs~496 μs 16 μs 1 00000~11111 512 μs~16384 μs 512 μs 

Comparison of the performance of the former three examples (opt):

Another example of 6 bits in total, shown in Table 7:

Wherein 2 bits indicate the TXOP unit: 8 μs/16 μs/32 μs/512 μs.

TABLE 7 B1B2 B3~B6 TXOP range Unit 00 0000~1111  0 μs~120 μs  8 μs 01 0000~1111 128 μs~368 μs 16 μs 10 0000~1111 384 μs~864 μs 32 μs 11 0000~1111  896 μs~8576 μs 512 μs 

Another example of 6 bits in total, shown in Table 8:

Wherein 2 bits indicate the TXOP unit: 16 μs/16 μs/32 μs/512 μs.

TABLE 8 B1B2 B3~B6 TXOP range Unit 00 0000~1111  0 μs~240 μs 16 μs 01 0000~1111 256 μs~496 μs 16 μs 10 0000~1111 512 μs~992 μs 32 μs 11 0000~1111 1024 μs~8704 μs 512 μs 

Another example of 6 bits in total, shown in Table 9:

Wherein 2 bits indicate the TXOP unit: 16 μs/16 μs/16 μs/512 μs.

TABLE 9 B1B2 B3~B6 TXOP range Unit 00 0000~1111  0 μs~240 μs 16 μs 01 0000~1111 256 μs~496 μs 16 μs 10 0000~1111 512 μs~752 μs 16 μs 11 0000~1111  768 μs~8448 μs 512 μs 

Example 4, Shown in Table 10

Fixed 64 μs granularity with 7 bit in total.

TABLE 10 B1~B7 TXOP range Unit 0000000~1111111 0 μs~8128 μs 64 μs

Example 5, Shown in Table 11

7 bits in total

2 bits indicate the TXOP unit: 4 μs/16 μs/64 μs/256 μs.

TABLE 11 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~124 μs  4 μs 01 00000~11111 128 μs~624 μs  16 μs 10 00000~11111 640 μs~2624 μs 64 μs 11 00000~11111 2688 μs~10624 μs 256 μs 

Example 6, Shown in Table 12

7 bits in total

2 bits indicate the TXOP unit: 8 μs/16 μs/32 μs/256 μs

TABLE 12 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs  8 μs 01 00000~11111 256 μs~752 μs 16 μs 10 00000~11111  768 μs~1760 μs 32 μs 11 00000~11111 1792 μs~9728 μs 256 μs 

Example 7, Shown in Table 13

7 bits in total

2 bits indicate the TXOP unit: 8 μs/16 μs/64 μs/256 μs

TABLE 13 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs  8 μs 01 00000~11111 256 μs~752 μs  16 μs 10 00000~11111 768 μs~2752 μs 64 μs 11 00000~11111 2816 μs~10752 μs 256 μs 

Example 8, Shown in Table 14

7 bits in total

2 bits indicate the TXOP unit: 8 μs/16 μs/64 μs/512 μs

TABLE 14 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs  8 μs 01 00000~11111 256 μs~752 μs  16 μs 10 00000~11111 768 μs~2752 μs 64 μs 11 00000~11111 2816 μs~18688 μs 512 μs 

Example 9, Shown in Table 15

7 bits in total

2 bits indicate the TXOP unit: 8 μs/32 μs/128 μs/512 μs.

TABLE 15 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs  8 μs 01 00000~11111 256 μs~1248 μs  32 μs 10 00000~11111 1280 μs~5248 μs  128 μs 11 00000~11111 5376 μs~21248 μs 512 μs

Example 10, Shown in Table 16

7 bits in total

2 bits indicate the TXOP unit: 8 μs/32 μs/64 μs/512 μs

TABLE 16 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs  8 μs 01 00000~11111 256 μs~1248 μs 32 μs 10 00000~11111 1280 μs~3264 μs  64 μs 11 00000~11111 3328 μs~19200 μs 512 μs 

Example 11, Shown in Table 17

7 bits in total

2 bits indicate the TXOP unit: 8 μs/8 μs/8 μs/256 μs

TABLE 17 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs 8 μs 01 00000~11111 256 μs~504 μs 8 μs 10 00000~11111 512 μs~760 μs 8 μs 11 00000~11111  768 μs~8704 μs 256 μs 

TXOP duration for ACK/BA/MBA

The TXOP duration field in HE-SIGA can also indicate the time duration for the ACK/BA/MBA immediately following the data PPDU. Shown in FIG. 3.

We can use 7 bits to indicate 1 ms with the unit of 8 μs, which can cover most of the ACK/BA/MBA frames with low MCS.

TABLE 18 B1~B7 TXOP range Unit 0000000~1111111 0 μs~1016 μs 8 μs

Or, in another example,

TABLE 19 B1~B7 TXOP range Unit 0000000~1111111 0 μs~2032 μs 16 μs

Example 12

As shown in Table 20, example 12 is has been disclosed by example 11, which excludes the entry 11111 in Table 17. TXOP in HE-SIGA can use 7 bits with 2 granularities, one is small and one is large granularity. For example, small granularity uses 8 μs to indicate the TXOP range from 0˜760 μs with 96 entries, and large granularity uses 256 μs to indicate the TXOP range from 768˜8448 μs with 31 entries. 2 bits indicate the TXOP unit: 8 μs/8 μs/8 μs/256 μs

TABLE 20 B1B2 B3~B7 TXOP range Unit 00 00000~11111  0 μs~248 μs 8 μs 01 00000~11111 256 μs~504 μs 8 μs 10 00000~11111 512 μs~760 μs 8 μs 11 00000~11110  768 μs~8448 μs 256 μs 

As the duration field in MAC header is in 1 us unit, there will be accuracy difference between duration in MAC header and TXOP in HE-SIGA. To avoid the over-protection issue that TXOP in HE-SIGA is large than duration in MAC header, the valid duration information indicated by the TXOP field in HE-SIGA shall be the largest feasible duration information that is smaller than or equal to the duration information indicated by the Duration field in a MAC header in the HE PPDU. Then TXOP in HE-SIGA is always less than the exact duration in MAC header with a delta_T, shown in FIG. 4, which relies on the granularity used. This cause a under-protection issue that TXOP in HE-SIGA can't cover the exact duration in MAC header.

To avoid the under-protection issue, we add the following rules:

(1) Assuming TXOP holder sends a soliciting frame (e.g. frame 0) with TXOP in HE-SIGA to be the value PHT_0. TXOP responder should transmit a responding frame (e.g. frame 1) no longer than PHT_0-SIFS_time, to avoid that the reception of responding frame at TXOP holder is interfered by OBSS STA which only decodes TXOP field in soliciting frame from TXOP holder and set NAV with PHT_0. Show in FIG. 5.

(2)Assuming TXOP holder receives a responding frame from TXOP responder with TXOP in HE-SIGA to be the value PHT_1. If TXOP holder transmits to the same TXOP responder, it should transmit another soliciting frame (e.g. frame 2) no longer than PHT_1-SIFS_time, to avoid that the reception of the soliciting frame (frame 2) at TXOP responder is interfered by OBSS STA which only decodes TXOP field in responding frame from TXOP responder and set NAV with PHT1. Shown in FIG. 6.

Note: These two rules apply to all example for TXOP encoding tables above.

The scheme of the embodiments is applicable to a WLAN network system. The following is a schematic diagram of an applicable scenario of the method in a wireless local area network provided by embodiments. As shown in FIG. 7 below, the WLAN network system may include an access station 101 and at least a station 102. In the WLAN network system, some stations (non-AP station or AP) may work as a TXOP holder, others may work as a responder, like shown in FIG. 4, 5, or 6.

An access point (AP, Access Point) may also be referred to as a wireless access point, a bridge, a hotspot, or the like, and may be an access server or a communications network.

A station (STA, Station) may be further referred to as a user, and may be a wireless sensor, a wireless communications terminal, or a mobile terminal, for example, a mobile telephone (or referred to as a “cellular” phone) that supports a WiFi communication function and a computer that has a wireless communication function. For example, the station may be a portable, pocket-sized, handheld, computer built-in, wearable, or in-vehicle wireless communications apparatus that supports the WiFi communication function, and exchanges communication data such as voice and data with a wireless access network.

A person skilled in the art knows, some communication equipment may include the both functions of the above STA and AP. It's not limited in the embodiments.

FIG. 8 is a schematic diagram of a data transmission apparatus (such as an access point, a station, a chip, or the like) provided in the embodiments. As shown in FIG. 8 below, the data transfer apparatus 1200 may be implemented as general bus architecture for the bus 1201. Depending on the particular application of the data transfer apparatus 1200 and the overall design constraints, the bus 1201 may include any number of interconnect buses and bridges. The bus 1201 couples various circuits, including a processor 1202, storage medium 1203, and a bus interface 1204. The bus 1201, the data transfer apparatus 1200 uses the bus interface 1204 to connect the network adapter 1205 and the like via the bus 1201. As shown in FIG. The network adapter 1205 may be used to implement the signal processing functions of the physical layer in the wireless local area network and transmit and receive the radio frequency signals via the antenna 1207. The user interface 1206 may connect a user terminal, such as a keyboard, a display, a mouse, a joystick, or the like. The bus 1201 may also be connected to various other circuits such as timing sources, peripherals, voltage regulators, power management circuits, etc., which are well known in the art and will not be described in detail.

The data transfer apparatus 1200 may also be configured as a general processing system that includes one or more microprocessors that provide processor functionality, and an external memory that provides at least a portion of the storage medium 1203, all of which are communicated via an external bus system The structure is connected with other supporting circuits.

Alternatively, the data transfer apparatus 1200 may be implemented using an ASIC (application-specific integrated circuit) having a processor 1202, a bus interface 1204, a user interface 1206, and at least a portion of a storage medium 1203 integrated in a single chip, or, The data transmission device 1200 may be implemented using one or more of an FPGA (Field Programmable Gate Array), a PLD (Programmable Logic Device), a controller, a state machine, gate logic, discrete hardware components, any other suitable Circuits, or any combination of circuits capable of performing the various functions described throughout this disclosure.

The processor 1202 is responsible for managing the bus and general processing (including executing the software stored on the storage medium 1203). The processor 1202 may be implemented using one or more general purpose processors and/or dedicated processors. Examples of processors include microprocessors, microcontrollers, DSP processors, and other circuits capable of executing software. Software should be broadly construed to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The storage medium 1203 is shown as being separate from the processor 1202, however, it will be readily apparent to those skilled in the art that the storage medium 1203 or any portion thereof may be located outside of the data transmission device 1200. For example, the storage medium 1203 may include a transmission line, a carrier waveform modulated with data, and/or a computer article separated from the wireless node, all of which may be accessed by the processor 1202 via the bus interface 1204. Alternatively, the storage medium 1203 or any portion thereof may be integrated into the processor 1202, which may be, for example, a cache and/or general purpose register.

The processor 1202 may perform the above-described embodiments, and will not be described herein.

It will be appreciated by those of ordinary skill in the art that all or part of the steps of implementing the method embodiments described above may be accomplished by program related hardware which may be stored in a computer-readable storage medium which, when executed, including the steps of the above-described method embodiment, and the aforementioned storage medium includes various kinds of media, such as a ROM, a RAM, a magnetic disk, or an optical disk, on which program codes can be stored.

The embodiments can be applied to wireless local area networks, including, but not limited to, Wi-Fi systems represented by 802.11a, 802.11b, 802.11g, 802.11n, and 802.11ac and also to next-generation Wi-Fi systems, Wireless LAN systems.

Of course, it may be applied to other possible wireless networks.

The following provides a number of embodiments provided by a simple language description:

An information transmission method for radio communication,

Generating, by a sending site, a PPDU carrying a TXOP field in the HE-SIGA of the PPDU, the TXOP field is used for notifying the other stations of the remaining time of the station usage channel, wherein the TXOP field can be indicated by different granularity;

sending the PPDU.

An information receiving method for radio communication,

receiving, a PPDU sent by a sending site, the HEOPA of the PPDU carrying a TXOP field for informing other stations of the remaining time of the station usage channel, wherein the TXOP field may be carried out at different granularity Instructions;

sending, a TXOP response frame according to the received PPDU.

The method according to embodiment 1 or 2, the TXOP field is indicated using two different granularity.

The method of embodiment 3, the TXOP field is indicated by two granularities of 8 μs and 256 μs.

The method of embodiment 4, wherein the TXOP field is 7 bits in length and includes 128 values; wherein 96 values are indicated by a granularity of 8 μs, the indicated TXOP range is 0 to 760 microseconds; 31 The number is indicated with a granularity of 256 μs and the indicated TXOP range is 768 to 8448 μs.

The method according to embodiment 2, further comprising:

the TXOP length of the TXOP response frame should be less than or equal to the length remaining after subtracting the SIFS time from the value represented by the TXOP field in the initiation frame of the station (TXOP origination station).

The method of embodiment 1, wherein the station sends a new TXOP initiation frame if the destination address of the new TXOP transmit frame matches the transmit address of the station that sent the previous TXOP response frame, the new TXOP transmission frame should be less than or equal to the length remaining after the SIFS time minus the value represented by the TXOP field in the TXOP response frame.

The method of embodiment 2, after receiving a PPDU sent by the sending site, replies to an ACK or BA, the ACK or BA comprising a duration field in the granularity representation, the duration field being represented by The time at which the other stations will be notified of the channel to be used.

A communication device comprising a memory and a processor, operable to perform methods such as 1, 3-5, 7.

A communication device comprising a memory and a processor, operable to perform methods such as 2, 3-5, 8. 

What is claimed is:
 1. A method for indicating a transmission opportunity (TXOP) duration in a wireless communication system, comprising: generating, by a first station, a physical layer protocol data unit (PPDU), wherein the PPDU includes a High Efficiency Signal field A (HE-SIGA), the HE-SIGA includes TXOP duration field, the TXOP duration field is used to indicate a TXOP duration which is remaining time for using a channel, the TXOP duration field comprises 7 bits in total, and the TXOP duration field includes a first part which indicates a granularity used to indicate the TXOP duration, and a second part which indicates the TXOP duration using the granularity indicated by the first part; wherein a first value of the first part indicates a first granularity, a second value of the first part indicates a second granularity, the first granularity is 8 μs, and the second granularity is 128 μs; and sending, by the first station, the generated PPDU.
 2. The method according to the claim 1, wherein the first part of the TXOP duration field has 1 or 2 bits.
 3. The method according to claim 1, wherein the TXOP duration is the remaining time for using the channel by a TXOP holder.
 4. The method according to claim 1, wherein the TXOP duration indicated by the TXOP duration field is smaller than or equal to a duration indicated by a Duration field in a MAC header in the PPDU.
 5. The method according to claim 1, wherein the method further comprises: receiving, by the first station, a responding frame, and a length of the responding frame should be less than or equal to a length remaining after subtracting short interframe space (SIFS) time from the TXOP duration indicated by the TXOP duration field.
 6. A method for indicating a transmission opportunity (TXOP) duration in a wireless communication system, comprising: receiving, by a second station, a physical layer protocol data unit (PPDU), wherein the PPDU includes a High Efficiency Signal field A (HE-SIGA), the HE-SIGA includes a TXOP duration field, the TXOP duration field comprises 7 bits in total, the TXOP duration field is used to indicate a TXOP duration which is remaining time for using a channel, and the TXOP duration field includes a first part which indicates a granularity used to indicate the TXOP duration, and a second part which indicates the TXOP duration using the granularity indicated by the first part; wherein a first value of the first part indicates a first granularity, a second value of the first part indicates a second granularity, the first granularity is 8 μs, and the second granularity is 128 μs; and obtaining, by the second station, the TXOP duration according to the TXOP duration field.
 7. The method according to the claim 6, wherein the first part of the TXOP duration field has 1 or 2 bits.
 8. The method according to claim 6, wherein the TXOP duration is the remaining time for using the channel by a TXOP holder.
 9. The method according to claim 6, wherein the TXOP duration indicated by the TXOP duration field is smaller than or equal to a duration indicated by a Duration field in a MAC header in the PPDU.
 10. The method according to claim 6, wherein the method further comprises: sending, by the second station, a responding frame, and a length of the responding frame should be less than or equal to a length remaining after subtracting short interframe space (SIFS) time from the TXOP duration indicated by the TXOP duration field.
 11. A communication apparatus comprising: at least one processor; and a non-transitory computer-readable storage medium coupled to the at least one processor and storing programming instructions for execution by the at least one processor, wherein the programming instructions instruct the apparatus to: generate a physical layer protocol data unit (PPDU), wherein the PPDU includes a High Efficiency Signal field A (HE-SIGA), the HE-SIGA includes a transmission opportunity (TXOP) duration field, the TXOP duration field comprises 7 bits in total, the TXOP duration field is used to indicate a TXOP duration which is remaining time for using a channel, and the TXOP duration field includes a first part which indicates a granularity used to indicate the TXOP duration, and a second part which indicates a TXOP duration using the granularity indicated by the first part; wherein a first value of the first part indicates a first granularity, a second value of the first part indicates a second granularity, the first granularity is 8 μs, and the second granularity is 128 μs; and send the generated PPDU.
 12. The apparatus according to the claim 11, wherein the first part of the TXOP duration field has 1 or 2 bits.
 13. The apparatus according to claim 11, wherein the TXOP duration is the remaining time for using the channel by a TXOP holder.
 14. The apparatus according to claim 11, wherein the TXOP duration indicated by the TXOP duration field is smaller than or equal to a duration indicated by a Duration field in a MAC header in the PPDU.
 15. The apparatus according to claim 11, wherein the programming instructions further instruct the apparatus to: receive, a responding frame, and a length of the responding frame should be less than or equal to a length remaining after subtracting short interframe space (SIFS) time from the TXOP duration indicated by the TXOP duration field.
 16. A communication apparatus comprising: at least one processor; and a non-transitory computer-readable storage medium coupled to the at least one processor and storing programming instructions for execution by the at least one processor, wherein the programming instructions instruct the apparatus to: receive a physical layer protocol data unit (PPDU), wherein the PPDU includes a High Efficiency Signal field A (HE-SIGA), the HE-SIGA includes a transmission opportunity (TXOP) duration field, the TXOP field comprises 7 bits in total, the TXOP duration field is used to indicate a TXOP duration which is remaining time for using a channel, and the TXOP duration field includes a first part which indicates a granularity used to indicate the TXOP duration, and a second part which indicates a TXOP duration using the granularity indicated by the first part; wherein a first value of the first part indicates a first granularity, a second value of the first part indicates a second granularity, the first granularity is 8 μs, and the second granularity is 128 μs; and obtain, the TXOP duration according to the TXOP duration field.
 17. The apparatus according to the claim 16, wherein the first part of the TXOP duration field has 1 or 2 bits.
 18. The apparatus according to claim 16, wherein the TXOP duration is the remaining time for using the channel by a TXOP holder.
 19. The apparatus according to claim 16, wherein the TXOP duration indicated by the TXOP duration field is smaller than or equal to a duration indicated by a Duration field in a MAC header in the PPDU.
 20. The apparatus according to claim 16, wherein the programming instructions further instruct the apparatus to: send, a responding frame, and a length of the responding frame should be less than or equal to a length remaining after subtracting short interframe space (SIFS) time from the TXOP duration indicated by the TXOP duration field. 